The present invention relates, in general, to band saw apparatus suitable for cutting relatively hard metal objects and, more particularly, relates to an apparatus and method for enhancing cutting rates, cutting precision and blade life by varying the force of the cutting edge of the blade per unit area of the workpiece during cutting
Various attempts have been made to enhance the cutting rate of a band saw when cutting hard materials. One approach is to form the band saw blade of a configuration which will induce pressure variations between the cutting edge of the blade and the workpiece being cut. Typical of such efforts is the apparatus set forth in U.S. Pat. Nos. 4,205,571, 4,195,543, 4,160,397 and 4,023,448. In these patents an endless band saw blade is formed with a varying height or side elevational profile so that, as the height variations of the blade pass over guide means, the blade is alternately displaced or urged toward and then permitted to move away from the workpiece. This alternate slight increase and decrease of the localized pressure of the cutting edge of the blade against the workpiece has been found to increase the efficiency of cutting and accordingly reduce the cutting time. This can be quite important in high production cutting of hard metallic materials.
While enhanced cutting efficiency is highly desirable, it would be even more advantageous if it could be achieved without the necessity of having a specially formed band saw blade. Additionally, it is inherent in connection with the use of a sinusoidal, stepped or otherwise specially formed blade that the same areas of the blade which project outwardly toward the workpiece the farthest will undergo the greatest amount of stress and wear. Thus, over the length of a band saw blade, all of the downwardly projecting areas will tend to wear first and to have the greatest potential for blade fatiguing stress risers.
It is possible to change specially formed blades to vary the amplitude of blade displacement and thus pressure applied, and it also is possible to vary the cutting speed to change the frequency of pressure variation. These changes, however, are not easily or quickly accomplished. For band saw apparatus in which the production runs are short and the materials being cut are changed frequently, for example, in a job-shop, repeated blade changing can be a substantial disadvantage.
Another approach to varying the pressure applied by a band saw blade during cutting is disclosed in U.S. Pat. No. 4,127,045. In this patent a band saw is shown which has a blade guiding assembly that is formed to displace the saw blade toward and permit movement away from the workpiece by a step cam and follower. The advantages of localized pressure variation without many of the disadvantages of a specially formed blade can be achieved.
The apparatus of U.S. Pat. No. 4,127,045 employs a feature which is well known in the cutting art, and partcularly in connection with power back saws and power grinders, namely, variation of the angle of cutting during the cut. MARVEL brand hack saws, produced by Armstrong-Blum Manufacturing Co. of Chicago, Ill., have for many years used a "Roll Stroke" blade motion which progressively raises one end of the saw blade while lowering the other as the blade is drawn though the work. Grinders similarly have been constructed in which the pivotal arm upon which the abrasive wheel is mounted is itself eccentrically mounted to displace the pivot point of the arm and thereby vary the area being cut.